(1) Field of the Invention
The present invention relates to a positive type actinic ray-decomposing and developing dry film formed from an actinic ray-decomposing and developing resin composition containing a resin having a urethane linkage, showing high sensitivity and good film-handling properties, and capable of forming a pattern which is useful in the formation of a circuit in an electronic device, a material for use in printing.
(2) Description of Background Art
A method of forming a photo-curable resist film which comprises coating or printing a liquid photo-curable resist composition onto a printed circuit board having a through-hole and/or non-through-hole (hereinafter may be simply referred to as a through-hole) according to a coating or printing method such as spray coating, roll coating, silk screen printing or the like, has well known in the art. However, the above methods had such problems that coating or printing of the liquid resist composition directly onto the printed circuit board makes it impossible to form a satisfactory resist film in the interior of the through-hole, resulting in that partial or complete dissolution in an etching solution of a conductive film such as copper, silver and the like in the interior of the through-hole during an etching step may cause to produce troubles such as breaking and the like.
For the purpose of protecting the through-hole from the etching solution, in the recent years, a positive type film resist formed by coating a positive type photo-decomposing and developing liquid resist composition onto a substrate has been used. As an example of the positive type photo-decomposing and developing liquid resist composition, a visible light-sensitive composition comprising a carboxyl group-containing polymer, a polyvinyl ether compound and a compound producing an acid by decomposition due to irradiation of an actinic ray is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 313134/94, 313135/94, 313136/94, 308733/94, 295064/64, 146552/95, and the like.
The above composition is such a photo-decomposing and developing composition that heating of a coating film formed from the composition takes place crosslinking due to addition reaction between carboxyl group and vinyl ether group so as to be insoluble in a solvent and an aqueous alkali solution, and that irradiation of an actinic ray thereonto and heating thereafter breaks down a crosslinked structure due to a catalytic action of an acid produced so that an irradiated area may be made soluble again in a solvent and an aqueous alkali solution.
However, a positive type dry film formed by a process which comprises coating the above-positive type photo-decomposing and developing composition onto a substrate such as polyethylene terephthalate and the like followed by drying, produced such problems that (1) because of unsatisfactory mechanical properties of the positive type photo-decomposing and developing coating film, cracking and separation from the substrate of the coating film take place on winding a dry film dried and formed as above, resulting in making difficult handling of the dry film, that (2) in a method of forming a positive type photo-decomposing and developing coating film onto the surface of a printed circuit board by use of a dry film, which method comprises facing and folding the positive type photo-decomposing and developing coating film onto the printed circuit board, heating the dry film so as to be laminated and separating the polyethylene terephthalate substrate from the positive type photo-decomposing and developing coating film, because of poor adhesion properties between the positive type photo-decomposing and developing coating film and the substrate, after the above separating step, the positive type photo-decomposing and developing coating film may partly or wholly remain on the surface of the polyethylene terephthalate substrate, and that (3) because of unsatisfactory mechanical properties of the positive type photo-decomposing and developing coating film, an erosion of the coating film with an etching solution may take place to be washed out, resulting in making it impossible to form a fine resist pattern.
As an example of a positive type photo-decomposing and developing dry film, Japanese Patent Application Laid-Open No. 506106/93 discloses a dry film photoresist prepared by forming a solid photo-decomposing and developing layer comprising a polymer having a photo-acid-unstable group and a photo-acid generator onto a flexible thin polymer film substrate. That is, the above dry film is such that the photo-acid-unstable group in the polymer may be decomposed by the action of an acid generated from the photo-acid generator or irradiation, so that an irradiated area only may be dissolved in a developing solution to provide a positive type image, but had such drawbacks as to be unable to form a fine image because of unclear correspondence of nondissolution or dissolution to a nonirradiated coating film area or an irradiated coating film area.